Embodiments of the present invention provided a system comprising: a plurality of speed controllers each configured to assume one or more ‘on’ states or one or more ‘off’ states, in a predetermined one or more on states each speed controller being configured to cause a vehicle to operate in accordance with a target speed value, in an off state each speed controller being configured not to cause a vehicle to operate in accordance with a target speed value, the system being configured wherein only one of the speed controllers may be in an on state at a given moment in time, the other one or more speed controllers being arranged to assume an off state when a speed controller is in an on state, the system being configured to delete from a speed controller memory or associated speed controller memory directly accessible by said speed controller, one or more target speed values employed by a speed controller that is not in an on state.